I ran an English BB for a while in my Swiss threaded Super Mirage. Cups had a little bit of play except when they were tightened against the shell.
The one time I jammed (that's the word) a BSC BB cup into a Swiss BB shell it was a tight fit, not loose.
Seems like there are some conflicting stories about this. I would think it would feel tighter because the thread pitch is finer on a swiss BB shell but the sheldon site, as well as some of you, say otherwise.
Here is the Mondia. Reynolds 531 with campy dropouts. I believe it is a early 80's (1980?) based on dropouts and the top tube cable guides. The serial number is 803942. I really like the aesthetics of it and am glad it doesn't have the crazy fade paint jobs I have seen. The pin striping is great and the chrome bits make it very classy in my opinion. I am going to make it an upright single speed for a while. I ordered some Nitto promenade bars and will get brown leather grips and brown B17.